Nanoporous structures produced from self-assembling molecules

ABSTRACT

Methods for producing nanoporous structures are provided. In the subject methods, two or more, e.g., first and second, different types of self-assembling molecules are combined with each other under conditions sufficient to produce a composite ordered structure from the two or types of molecules. A feature of two or more molecules that are combined in this first step is that a portion of the molecules include cross-linking functionalities not found in the other portion of the molecules. The resultant self-assembled composite structure is then subjected to conditions sufficient for cross-linking of the portion of the molecules that includes the cross-linking functionalities to produce a stabilized composite structure. Finally, the remaining non-cross-linked molecules of the stabilized composite structure are separated from the stabilized composite structure to produce a nanoporous structure. Also provided are nanoporous structures produced according to the subject methods, articles of manufacture that include the same, as well as kits for use in practicing the subject methods.

INTRODUCTION

1. Field of the Invention

The field of this invention is self-assembling molecules andnanostructures produced thereby.

2. Background of the Invention

Molecular self-assembly has been defined as “the spontaneous associationof molecules under equilibrium conditions into stable, structurallywell-defined aggregates joined by noncovalent bonds.” Whitesides et al.,Science (1991) 254:1312-1319. Many examples of self-assembly occur inbiology, including amphiphilic bilayers in cell membranes, the T4 phageparticle, and the transmembrane toxin α-hemolysin. One of the mostimportant aspects of self-assembly is the fact that the final biologicalstructures are generally self-healing and relatively defect-free. Thisfeature is a result of the thermodynamic processes that drive theself-assembly process. In addition, the aforementioned biologicalstructures spontaneously assemble in the correct order and into thecorrect configuration without the need for complex atom-by-atomsynthesis. The above attributes of biological self-assembly are some ofthe motivating factors that have prompted researches to attempt to mimicself-assembly systems in the laboratory via synthetic routes.

For the purposes of nanofabrication, chemical self-assembly has severaladvantages. One advantage is that nanoscale objects are synthesizedspontaneously, without the need for expensive or elaborate equipment.Another advantage is that construction of nanostructures usingatom-by-atom protocols can be extremely time consuming and resourceintensive, if not impossible to perform.

While self-assembly of nanostructures is of great interest, the majorityof work to date has focused on the self-assembly of solidnanostructures. In certain applications, porous nanostructures aredesired. While attempts to produce porous nanostructures viaself-assembly protocols have been made, such have not been completelysuccessful. For example, the porosity of such structures may beinconsistent, the pore diameter may be too large, etc.

As such, there is a need for nano-objects and durable membranestructures with internal nanopores offering the characteristics ofelectrical reliability, as well as consistent overall size and porediameter. In addition, there is also a need for durable nanoporousmembrane structures. The present invention satisfies these, and other,needs.

Relevant Literature

Articles of interest include: Gunther & Stupp, Langmuir (2001)17:6530-6539; Hartgerink et al., Proc. Nat'l Acad. Sci. USA (2002) 99:5133-5138; Huggins et al., Macromolecules (1997) 30: 5305-5312; Hulteenet al., J. Am. Chem. Soc. (1998) 120: 6603-6604; Hwang et al., Proc.Nat'l Acad. Sci. USA (2002) 99: 9662-9667; Jenekhe et al., Science(1999) 372-375; Jenekhe et al., Science (1998) 279: 1903-1907; Moore andStupp, J. Am. Chem. Soc. (1992) 114: 9; Moore & Stupp, Polymer Bulletin(1988) 19: 251-256; Muthukumar et al., Science (1997) 277:1225-1232;Stupp et al., ACS Polymer Preprints (1989) 30: 396-397; Stupp et al.,Science (1993) 259:59-63; Stupp et al., Science (1997) 276: 384-389;Stupp et al., Science (1997) 277: 1242-1248; Stupp et al., J. am. Chem.Soc. (1995) 117: 5212-5227; and Zubarev et al., Science (1999)283:523-526.

SUMMARY OF THE INVENTION

Methods for producing nanoporous structures are provided. In the subjectmethods, two or more, e.g., first and second, different types ofself-assembling molecules are combined with each other under conditionssufficient to produce a composite ordered structure from the two ortypes of molecules. A feature of two or more molecules that are combinedin this first step is that a portion of the molecules includecross-linking functionalities not found in the other portion of themolecules. The resultant self-assembled composite structure is thensubjected to conditions sufficient for cross-linking of the portion ofthe molecules that includes the cross-linking functionalities to producea stabilized composite structure. Finally, the remainingnon-cross-linked molecules of the stabilized composite structure areseparated from the stabilized composite structure to produce ananoporous structure. Also provided are nanoporous structures producedaccording to the subject methods, articles of manufacture that includethe same, as well as kits for use in practicing the subject methods.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1 and 2 provide structures of representative self-assemblingmolecules that can be employed in methods of the subject invention.

FIGS. 3A-3B and 4A to 4B provide schematic drawings of representativestructures that can be prepared according to the subject methods.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Methods for producing nanoporous structures are provided. In the subjectmethods, two or more, e.g., first and second, different types ofself-assembling molecules are combined with each other under conditionssufficient to produce a composite ordered structure from the two ortypes of molecules. A feature of two or more types of molecules that arecombined in this first step is that a portion of the molecules includecross-linking functionalities not found in the other portion of themolecules. The resultant self-assembled composite structure is thensubjected to conditions sufficient for cross-linking of the portion ofthe molecules that includes the cross-linking functionalities to producea stabilized composite structure. Finally, the remainingnon-cross-linked molecules of the stabilized composite structure areseparated from the stabilized composite structure to produce ananoporous structure. Also provided are nanoporous structures producedaccording to the subject methods, articles of manufacture that includethe same, as well as kits for use in practicing the subject methods.

Before the subject invention is described further, it is to beunderstood that the invention is not limited to the particularembodiments of the invention described below, as variations of theparticular embodiments may be made and still fall within the scope ofthe appended claims. It is also to be understood that the terminologyemployed is for the purpose of describing particular embodiments, and isnot intended to be limiting. Instead, the scope of the present inventionwill be established by the appended claims.

In this specification and the appended claims, the singular forms “a,”“an” and “the” include plural reference unless the context clearlydictates otherwise.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range, and any other stated or intervening value in thatstated range, is encompassed within the invention. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges, and are also encompassed within the invention, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the invention.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this invention belongs. Although any methods, devicesand materials similar or equivalent to those described herein can beused in the practice or testing of the invention, the preferred methods,devices and materials are now described. Methods recited herein may becarried out in any order of the recited events which is logicallypossible, as well as the recited order of events.

All patents and other references cited in this application, areincorporated into this application by reference except insofar as theymay conflict with those of the present application (in which case thepresent application prevails).

In further describing the subject invention, the subject methods ofmaking nanoporous structures, as well as the reagents employed thereinand resultant structures thereof, are reviewed first in greater detail,followed by a review of representative applications in which the subjectmethods and products thereof find use, as well as kits of reagents thatfind use in practicing the subject methods.

Methods

As summarized above, the subject invention provides methods of makingnanoporous structures. Nanoporous structures produced by the subjectmethods are structures that include one or more pores, where the poresare nanoscale in that they have diameters described in terms ofnanometers. The structures produced by the subject methods are reviewedin greater detail below.

A feature of the subject methods is that the subject nanoporousstructures are produced using a self-assembly protocol, in which atleast two different self-assembling or self-organizing molecules arecombined under self-assembly conditions to produce an initial compositestructure, where the initial composite structure is a regular or orderedstructure made up of the two or more self-assembling molecules. In otherwords, the resultant structure is a stable, well-defined aggregatestructure in which the two or more self-assembling molecules thereof areheld together by non-covalent bonds. The initial composite structure isthen stabilized by subjecting it to cross-linking conditions, such thata subpopulation of the constituent molecules covalently bond to oneanother to produce a shape invariant composite structure. The resultantstabilized shape invariant composite structure is then subjected toconditions sufficient to separate the non-covalently bonded constituentmolecules thereof from the remainder of the structure, resulting in theproduction of the desired nanoporous structure. Each of these compositesteps is now described below separately in greater detail.

Production of Composite Structure by Self-Assembly

As summarized above, the first step in the subject methods is to producea regular, uniformly ordered composite structure from two or moreself-assembling or self-organizing molecules, i.e., by a self-assemblyprocess. In performing the first step of the subject methods, two ormore different types of molecules are combined together under conditionssufficient for the molecules to self-assemble or self-organize into aregular or ordered structure. By regular or ordered structure is meantan aggregate of molecules having a regular or defined order, e.g., aplanar structure, a nanostructure, etc., where the constituent moleculesof the composite structure are held together by non-covalentinteractions.

The regular or ordered structure produced upon combination andsubsequent self-assembly or self-organization of the two or moreself-assembling or self-organizing molecules may be any of a number ofdisparate configurations, depending on the nature of the self-assemblingmolecules employed to make the structure. Representative configurationsof interest include, but are not limited to: two-dimensional sheets ormembranes; particulate nanostructures (e.g., “mushroom” shapedparticulate nanostructures); rods, discs, stacks, cylinders, spheres,and the like.

As indicated above, in the first step at least two or more differenttypes of molecules that self-assemble or self-organize with each otherto produce the desired composite structure are combined under conditionssufficient for self-assembly to occur. The number of different ordistinct types of self-assembling molecules that are combined in thisfirst step may vary, where the number may range from about 1 to about10, e.g., from about 1 to about 5, where the number is 2 or 3, and moreoften 2, in many embodiments.

A feature of the 2 or more constituent types of molecules that arecombined in the initial step is that a portion of the constituentmembers include one or more functionalities that provide for covalentbonding or cross-linking to one another (also known in the art as“stitching”), as described below in review of the second step of thesubject methods, while the remainder portion of the constituent memberslack such functionalities found in members of the first portion. Forexample, where first and second self-assembling molecules are employedin the first step, each of the identical “first” molecules includes oneor more covalent bonding functionalities that provides for the abilityto cross-link the molecules, as described below, while each of theidentical “second” molecules lacks these one or more functionalities.

In addition to depending on the specific nature of the two or moreself-assembling molecules, e.g., the first and second self-assemblingmolecules, the composite structure that is self-assembled therefrom isalso dependent on the proportion of the two or more different types ofmolecules that are combined with each other in the first step. Where apopulation of first and second molecules are combined in this firststep, the first and second molecules are, in certain representativeembodiments, combined in a molar ratio ([first]/[second]) that may rangefrom about 1/100 to about 30/100, such as from about 4/100 to about20/100, including from about 10/100 to about 15/100.

As mentioned above, the collection of two or more different types ofmolecules employed in the first step includes a portion of moleculesthat include a covalent bonding or cross-linking functionality and aportion of molecules that lack this functionality or thesefunctionalities. Additional differences that may be present betweendifferent constituent members of the employed population of two or moredifferent molecules may include, but are not limited to: specificterminating functional groups, pendant groups, individual blocks used inthe diblock or triblock molecule, and the like. For example, the portionof molecules that do not include a cross-linking functionality mayinclude additional terminal functionalities that promote theirassociation with each other, that promote there separation from thestabilized composite structure, as described below, etc. In yet anotherrepresentative example, the portion of molecules that does include across-linking functionality may further include functionalities that areexploited in the use of the final product, e.g., pore liningfunctionalities that impart desirable properties to the pores of theresultant structure, such as surface transport enhancement, etc.

Despite the above differences, including optional differences, among thepopulation of two or more different kinds of self-assembling molecules,the different types of self-assembling molecules are, in certainembodiments, sufficiently similar such that they do self-assemble ororganize into the desired composite structure. As such, in certainembodiments all of the molecules of the two or more different moleculeshave a common backbone or framework structure, where the only differenceamong the different types of molecules is, e.g., the presence or absenceof a cross-linking functionality, the presence or absence of terminalfunctionalities, etc.

While the nature of the different molecules employed to self-assemblethe composite structure may vary, in certain embodiments the moleculesare elongated linear molecules, that may or may not include one or morebranches, where the molecules may range in length from about 4nanometers to about 50 nanometers, usually from about 5 nanometers toabout 10 nanometers in certain embodiments. The molecular weight of themolecules may vary, but in certain embodiments ranges from about 500g/mol to about 5000 g/mol, such as from about 1500 g/mol to about 2500g/mol. In many embodiments, the molecules are organic molecules, ranginganywhere from about 75 to about 300 carbon atoms, such as from about 125to about 150 carbon atoms, where the molecules often include one or moreof, including a plurality of different features, e.g., heteroatoms,cyclic structures, including aryl moieties, sites of unsaturation, polargroups, either within or pendant to the main chain, and the like.

In certain embodiments, the different types of molecules employed aremultiblock polymers that include two or more different domains or blocksin linear configuration, where each of the two or more different blocksworks in concert to provide for the desired self-assembly and/orcrosslinking functionality. For example, one can have triblock structuremolecules that include terminal blocks that provide for self-assembly ororganization with other molecules, limitation of the size of theaggregate formed with other molecules, etc, and an internal block thatdoes or does not include a crosslinking functionality.

Where elongated organic molecules are employed in the self-assemblyprocess, they may include functionalities at one or more termini thatimpart desired properties in the structures produced from theself-assembling molecules. For example, hydrophilic functionalities,such as —OH, —COOH, and the like, may be present at termini so that theresultant structures are soluble in aqueous environments, adhere well tohydrophilic surfaces, etc. Alternatively, hydrophobic moieties may bepresent at termini where in the final structure the hydrophobic surfacesare desired. Hydrophobic moieties of interest include, but are notlimited to: —CF₃, —CH₃, —CH₂CH₃, Phenyl, and the like.

A number of different types of self-assembling organic molecules areknown to those of skill in the art, and may be employed, e.g., eitherdirectly or modified (e.g., by removal of cross-linkingfunctionalities), in the subject methods. As mentioned above, thespecific nature of the molecules employed in the composite structuregeneration step of the subject methods depends on the desiredconfiguration of the composite structure. Where the composite structureto be produced in the first step is a two-dimensional sheet or membrane,the two or more different molecules that are employed, e.g., the firstand second molecules employed, are ones that self-assemble to producethe desired planar structure, e.g., membrane or sheet. A variety ofdifferent molecules are known to spontaneously form two-dimensionalsheets, where such molecules include, but are not limited to thosedescribed in: Huggins et al., Macromolecules, 30 (18) 5305 (1997);Stupp, Son, Lin, Li, Science 259, 59(1993); Stupp et al, J. Am. Chem.Soc. 117, 5212 (1995); and the like.

There are several classes of materials that can form two-dimensionalsheets. One type of layered structures is formed by amphiphiles thatpolymerize upon dispersal in water. Examples of these compounds include,but are not limited to, those found in the following references: (1) Hubet al. Chem. Int. Ed. Engl. 1980, 19, 938 (2) Kuo, et al., Langmuir1991, 7, 584 (3) Asakuma et al., J. Am. Chem. Soc. 1991, 113, 1749.Another type of layered structure is formed by molecules that forminfinite 2D networks at an oil-water interface. Descriptions ofrepresentative compounds of these embodiments can be found in: (1)Rehage, et al., Makromol. Chem. 1988, 189, 2395; and (2) Dubalt, et al.,J. Phys. Chem. 1975, 79, 2254. One common factor in these types ofsystems is the fact that they are not shape-persistent. In other words,if the confining boundary is removed, then the 2D shape collapses. Thereare however, several types of molecules that form shape-persistent 2Dsheets. One such system consists of a bifunctional molecule containingacrylate and nitrile groups, such as the compoundsdescribed in detail byStupp et al. J. Am. Chem. Soc. 1995, 117, 5212-5227. Having twofunctional groups in the backbone of the constituent molecules helpsensure formation of a sheet. With only one functional group, themolecules would form a comb polymer, which is related to a linear chain.Another characteristic of shape persistent systems is the fact that ifthey do not posses D_(∞h) symmetry then they need to have enoughorientational order to ensure that the reactive molecules are indistinct planes. Another characteristic of these shape-persistentsystems is that the two reactive groups within the molecule need to befar enough apart so that reactive groups from one plane do notcross-react with reactive groups in the other plane.

Another 2D sheet structure of interest includes that described inHuggins et al., Macromolecules 1997, 30, 5305-5312. In this reference, aprecursor molecule that contained diacetylene functional groups as wellas other functional groups that were capable of forming hydrogen bondswas employed. In this specific situation, the groups that form hydrogenbonds play a role in the molecular stitching reaction that helps thesystem maintain its 2D sheet-like nature. These molecules fulfill thesame criteria as those described in the article by Stupp et al. supra.The reactive groups, in this case the diacetylene and the OH groups, arefar enough apart to ensure that 2D polymers rather than combs or laddersare formed. There is also the required amount of orientational order andrigidity.

These examples illustrate the fact that a variety of functional groupscan be used to create the stitching reactions that help create theshape-persistent 2D sheets. If the 3 general criteria describedpreviously are satisfied, then other reactive groups could besubstituted for the ones described in the previous references.

Of particular interest in certain representative embodiments are thelinear oligomeric compounds depicted in FIGS. 1 and 2. First oligomer 4of FIG. 1 is an oligomer prepared from monomers 3, 2 and 1. Theoligomers of FIG. 1 and the preparation thereof are described in Moore &Stupp, J. Am. Chem. Soc. (1992) 114: 9; and Stupp et al., Science (1993)259:59-63. Second oligomer 5 of FIG. 2 is an oligomer of monomers 1B, 2Band 3B. The preparation of the oligomer and monomer components thereofshown in FIG. 2 is readily practiced by one of skill in the art, basedon knowledge of the art, including the above specific referencesconcerning the oligomer and monomer reagents of FIG. 1.

As can be seen in FIG. 1, the oligomeric compound 4 is made up of threeblock components, i.e., 1, 2 and 3. Component 1 includes a reactivecyano group that is employed in cross-linking to covalently bondadjacent first molecules 4 together in the cross-linking step. Component2 is a short rod-coil monomer that, in the context of compound 4,provides rigidity and layer forming properties. Component 3 includes anend group, e.g., a vinyl moiety, which can be polymerized in order tocovalently cross-link adjacent layers of the molecules together.

Second oligomeric molecule 5 shares the same basic structure as firstoligomeric molecule 4. However, second oligomeric molecule 5 lacks thecyano and vinyl cross-linking functionalities present in first molecule4, and includes methyl moieties in place of these functionalities. Incertain embodiments, the terminal methyl group may be replaced withother groups that promote a desired organization of the compositestructure, e.g., —CF₃, —CH₃, —OH, —COOH, —CN, etc.

The above described embodiment produces a two-dimensional sheetstructure, as shown in FIG. 3, which upon phase separation results inthe production of a porous two-dimensional sheet as shown in FIG. 3B.

In a second representative embodiment, the two or more differentmolecules employed to prepare the composite structure in the initialstep are molecules that self-assemble into regular or definednano-objects. In these embodiments, the two or more self-assemblingmolecules may be chosen so that the molecules self-assemble into definedor ordered nano-objects of narrow polydispersity, e.g., from about1.0-1.5, including from about 1.05 to about 1.2, such as from about 1.06to about 1.1.

In a specific representative embodiment of interest, the first andsecond molecules are molecules that have been referred to in the art astriblock rodcoil molecules. Such molecules typically include a firstblock that provides for aggregation and crystallization of themolecules, e.g., through self-assembly. The second block provides forthe crosslinking functionality in the first type of molecule, whichcross-linking functionality is absent in the second type of molecule. Ablock of particular interest is one that includes one or more sites ofunsaturation, such as a random sequence of butadiene units. The thirdblock provides diversity to the molecules, which limits crystal growthin three dimensions, as well as steric elements that limit the size ofthe aggregates that are formed upon self-assembly. A representativeblock of interest is oligostyrene.

Of particular interest as first molecules in certain embodiments are thetriblock rodcoil molecules as described in Zubarev et al., Science(1999) 283:523, where a representative structure from this reference is:

As stated above, the second molecules in these embodiments share thesame backbone as the first molecules, but lack the crosslinkingfunctionalities, e.g., the carbon-carbon double bonds of the secondblock of the first molecules.

The above specific examples of different pairings of first and secondmolecules are merely representative of the different types ofself-assembling molecules that may be employed in the subject invention.Others pairings or grouping of molecules will become readily apparent tothose of skill in the art upon reading the present disclosure, and suchfall within the scope of the present invention.

Additional pairings of self-assembling molecules of interestmay satisfyseveral important criteria. Within the miniature triblock polymer, thestiff rod-like segment may chemically exclude the flexible spacer (andassociated cross-linking groups) as well as the flexible coil. Thisfeature can be achieved by making the flexible spacer and the flexiblecoil chemically diverse and aperiodic. In other words, if the flexiblecoil is synthesized from styrene monomers through living anionicpolymerization, the result will be a random sequence of meso and racemicdiads. Additionally, if isoprene is used as the basis of the flexiblecoil, then the result will be a mixture of 1,4 and 3,4 isomers alongwith 1,2 units. This mix of isomers in both cases, along with a narrowmolecular weight distribution (i.e. similar to a poisson distribution orslightly narrower) helps ensure that the resulting self-assembledmolecules form discrete objects rather than a 3D crystal. It is alsoimportant that the rod-like segments have a very high tendency toaggregate. In the previous examples, this was achieved by using rod-likesegments based on biphenyl ester groups which have a tendency toaggregate as a result of π-π overlap. The attractive force that existsamong the rod segments balances the repulsive force that exists amongthe flexible coil segments. This helps limit the size of the resultingnano-object. A specific example of another type of pairing is describedin research conducted by Cho et al. Macromolecules 2002, 35, 4845, suchas. The molecular structure of these molecules is shown below:

Although this system is based on modification of polymers with sidechains, it does give examples on other types of flexible coils andcomponents that are of interest to produce a linear triblock moleculefor use in the present methods. One could use the biphenyl estersegments again for the rigid block and substitute a PPO based moleculefor the flexible coil. Since PPO units have a smaller cross-sectioncompared with styrene units, the resulting nanostructures would likelyhave a different size. This would be a result of a change in the balanceof repulsive force among coil segments and attractive forces among rods.Molecules with a smaller cross-section would be able to pack at agreater density resulting in a nano-object that would likely be larger.To this structure (i.e. a combination of PPO and biphenyl groups), onewould need to add a flexible spacer, such as polyisoprene. To thisstructure, one would then modify a portion of the molecules so that theycontained a reactive group that is capable of cross-linking andstitching part of the structure together. Examples of some groups thatare capable of crosslinking include acrylate and nitrile groups. Doublebonds could also be used as pendant groups to provide an additional typeof site for cross-linking or stitching reactions.

Another rigid-rod and flexible coil system is described by Jenekhe etal. Science 1998, 279, 1903-1907; and in Jenekhe et al., Science 1999,283, 372-375. such as the structure shown below:

The structures described therein may be converted to miniature triblockmolecules by decreasing the length of each block and then by adding aflexible spacer between the rigid rod and the flexible coil systemdescribed in these references. Their system is based on flexible coilsof polystyrene and rod-like blocks composed of polyquinoline. Theflexible spacer that would then be added to such a system would eitherhave a reactive group or not, depending on whether it is a first orsecond type of molecule. Other rigid rods of potential interest wouldinclude blocks based on: polyacetylene (PA), poly(p-phenylene vinylene)(PPV), poly(p-phenylene) (PPP), polythiophene (PT) and polypyrrole(PPy). The relative amount of attraction between the rods and theirability to pack and crystallize would affect the resulting size of thenanostructure when combined with the degree of repulsion found among theflexible coil molecules.

As indicated above, in the first step of the subject methods, the two ormore self-assembling molecules are combined in the appropriate amountsunder conditions sufficient for the first and second molecules toself-assemble or self-organize into the initial composite structure. Theconditions under which the subject molecules are combined will varydepending upon the nature of the specific molecules being employed.Where desired, the molecules may be combined with agitation to uniformlymix or combine the molecules.

The molecules are typically present in a suitable solvent. Solvents ofinterest may be aqueous or non-aqueous, organic or inorganic, includingpolar and non-polar, solvents. Solvents of particular interest include,but are not limited to: methanol, ethanol, ethyl acetate, acetonitrile,chloroform, tetrahydrofuran and toluene.

The combined molecules in the appropriate solvent are typicallymaintained at a temperature and for a time sufficient for the desiredcomposite structure to form. Typically, the molecules are maintained ata temperature ranging from about 150° C. to about 300° C., such as fromabout 200° C. to about 250° C., and for a time ranging from about 30minutes to about 4 hours, such as from about 1 hour to about 2 hours.

Under such conditions, the first and second molecules self-assemble intoregular, ordered composite structures. As indicated above, the resultantcomposite structures may have a number of different configurations,depending on the particular molecules employed to make the structures,the conditions of self-assembly, and the like. A feature of theresultant composite structures is that they are made up of bothmolecules that include a cross-linking functionality, and molecules thatlack a cross-linking functionality. Depending on the nature of themolecules that lack the cross-linking functionality, in certainembodiments, these molecules may be clustered together within the largercomposite structure, such that the resultant composite structure hasregions that are rich in second molecules and regions that are poor insecond molecules.

Stabilization of the Composition Structure into a Shape InvariantStructure

As summarized above, in the next step of the subject methods, theresultant composite structure is stabilized to produce a shape invariantcomposite structure. The composite structure produced in the first stepis converted to a shape invariant structure, i.e., a stabilizedstructure that is not fluid, where the constituent molecules arecovalently bonded to one another, by subjecting the composite structureto a stimulus capable of causing the cross-linking or covalent bondingfunctionalities of a portion of the molecules making up the compositestructure to produce covalent bonds between the molecules of thisportion, i.e., to cross-link or stitch together those molecules thatinclude the appropriate cross-linking functionality. The stimulus may bea variety of different types of stimuli, depending on the nature of themolecules, where representative stimuli of interest include, but are notlimited to: addition of a chemical agent, temperature change, pHmodulation, change of solvent, and the like. For example, wheretemperature change is the stimulus employed to crosslink a portion ofthe molecules of the composite structure, the temperature of thestructure may be raised to temperature of from about 150° C. to about300° C., such as from about 200° C. to about 250° C., for a period oftime ranging from about 30 minutes to about 4 hours, such as from about1 hour to about 2 hours. The above step results in the production of astabilized composite structure in which a portion of the constituentmolecules, e.g., the first molecules in a composite structure made up ofpopulations of first and second molecules, are covalently bonded to eachother, i.e., are cross-linked, such that the composite structure is nowa shape invariant structure. A feature of the resultant shape invariantstructures is that a portion of the constituent molecules making up thestructure that lacks the covalent bonding functionality found in theother portion of the constituent molecules, e.g., the second molecules,is still present in the structure. This non-covalently bonded ornon-crosslinked portion of sub-population of the composite structure isthen separated from the remainder of the composite structure in thefinal step of the subject methods.

Separation of the Non-Covalently Bonded Molecules from the ShapeInvariant Structure

In the next step of the subject methods, that portion of the moleculesmaking up the composite structure are removed or separated from theremainder of the stabilized composite structure, to produce the desirednanoporous composite structure. The non-covalently bonded molecules ofthe stabilized composite structure may be separated from the remainderof the structure using any convenient protocol.

In many embodiments, the composite structure is placed in a solvent intowhich the second molecules dissolve out of the composite structure. Forexample, the composite structure may be immersed in a solvent in whichthe second molecules are highly soluble, resulting in the moleculesdissolving out of the composite structure. Solvents of interest for thisparticular embodiment include those described above, and will be chosenwith respect to the specific nature of the second molecule to bedissolved out.

Dissolution of non-covalently bonded molecules out of the compositestructure results in the production of an object in which pores arepresent where the non-covalently bonded molecules used to reside priorto the separation step. As such, the above-described methods result inthe production of a nanoporous structure that has a regular order ororganization and includes one or more, often a plurality of nanopores.By “nanopore” is meant a pore or passage through the structure that hasa nanoscale inner diameter, where the inner diameter ranges, in manyembodiments, from about 1 to about 20 nm, such as from about 1 to about2 nm, where a feature of the structures

produced by many embodiments of the subject methods is that thenanopores have inner diameters that are less than about 5 nm, e.g., theydo not exceed about 5 nm. A feature of the resultant nanoporousstructures are that they are stable, in that the constituent moleculemembers are covalently bonded or crosslinked to one another, such thatthe structure is not fluid and not readily disrupted.

The subject methods result in the production of nanoporous structures,as described above, of consistent size and consistent porosity, in thatwhile the methods result in the production of a population of structuresas the same time, the resultant population has a narrow polydispersity,in terms of variations in size of the resultant structures, variationsin porosity of the resultant structures, variations in pore diameter ofthe resultant structures, etc.

Utility

The nanoporous structures produced according to the subject inventionfind use in a number of different applications, including, but notlimited to, electronic applications, analytical applications andbiotechnology applications.

Specific representative electronics applications in which the structuresproduced according to the subject invention may find use include, butare not limited to: sensors, waveguidesand the like.

Analytical applications in which the subject nanoporous structures mayfind use are also varied, as a number of different analyticalapplications are currently known that employ nanopore devices, where theproduct nanoporous structures of the present invention may be used asnanopore elements in such devices, e.g., in place of the α-hemolysincomponent of such devices. Nanopore devices in which the subjectstructures may find use, include but are not limited to, those describedin U.S. Pat. Nos. 6,267,872; 6,362,002; 6,428,959; and 6,465,193; thedisclosures of which are herein incorporated by reference.Representative devices are also described in: Kasianowicz et al., Proc.Nat'l Acad. Sci. USA (1996) 93:13770-13773; Akeson et al., Biophys. J.(1999) 77:3227-3233; Meller et al., Proc. Nat'l Acad. Sci. USA (2000)97:1079-1084; Bayley et al., Nature (2001) 413: 226-230 and Li et al.,Nature (2001) 412: 166-169. As such, the subject structures may find usein devices that analyze nucleic acids, such as double and singlestranded nucleic acid characterization applications, e.g., nucleic acidsequencing applications.

Also of interest are biotechnology applications, in which the subjectstructures are used to modulate or alter biological systems. Forexample, the subject structures may be employed as artificial orsynthetic pore forming structures in cell walls, etc.

Accordingly, the structures produced by the subject methods find use ina variety of different applications, where the above providedapplications are merely representative of the multitude of differentapplications in which the subject structures find use.

Kits

Also provided are kits and systems for use in practicing the subjectinvention, where such kits may comprise containers, each with one ormore of the various reagents/compositions utilized in the methods, wheresuch reagents/compositions typically at least include the two or moreself-assembling molecules that may be employed in the subject methods.The kits may further include a number of additional components, e.g.,solvents for use in the self-assembly step, solvents employed in theseparation step, etc.

Finally, the kits may further include instructions for using the kitcomponents in the subject methods. The instructions may be printed on asubstrate, such as paper or plastic, etc. As such, the instructions maybe present in the kits as a package insert, in the labeling of thecontainer of the kit or components thereof (i.e., associated with thepackaging or sub-packaging) etc. In other embodiments, the instructionsare present as an electronic storage data file present on a suitablecomputer readable storage medium, e.g., CD-ROM, diskette, etc.

The following examples are offered by way of illustration and not by wayof limitation.

EXPERIMENTAL

The necessary steps for the basic synthesis of the mushroom-shapedstructure are described in several references. See e.g., M. Szwarc,Carbanion, Living polymers, and Electron Transfer Processes,Wiley-Interscience, New York, 1968; M. Morton, Anionic polymerization:Principles and Practice, Academic Press, New York, 1983; P. J. Manson,Polym. Sci. Polym. Chem. Ed. 18, 1945 (1980)] [R. P. Quirk and W. C.Chen, Makromol. Chem. 22, 85 (1989); and J. S. Moore and S. I. Stupp,Macromolecules 23, 65 (1990). A living anionic polymerization reaction(Szwarc) using a small amount of styrene monomer is used to create therandom coil portion of the miniature triblock molecule. Using only asmall amount of styrene monomer insures that the resulting structure hasa low degree of polymerization. The flexible spacer, comprised ofisoprene for example, can be synthesized by adding isoprene monomer tothe reaction mixture. (M. Morton) These compounds will insert themselvesbetween the living anion and the lithium ion. The result will be a shortchain of polyisoprene, in different isomeric configurations. To stop theliving anionic polymerization reaction, CO₂ is added to the reaction.This adds a carboxyl group at the end of the chain that can be used as areactive site for further reactions. [P. J. Manson] At this point, theresulting structure represents a diblock molecule, a combination of therandom coil and the flexible spacer. The building blocks for thebiphenyl ester segments can be made in a manner similar to thatdescribed in Huggins et al., Macromolecules 1997, 30, 5305-5312.Briefly, 4′-hydroxy-4-biphenylcarboxylic acid (4 g, 18.67 mmol) andsodium hydroxide (1.64 g, 41.1 mmol) is dissolved in 50 mL of water andethanol (8 mL) at −10° C. Methyl chloroformate (1.73 mL, 22.4 mmol) isthen added to the solution at a temperature of −5° C. The resultant mixis then stirred for 40 min., following which a solution of water andhydrochloric acid in a 1:1 ratio is added until the entire solutionbecomes acidic. The resulting precipitate is collected by vacuumfiltration, washed multiple times with distilled water and then dried. Amolecule that can be used as the rigid rod component of the triblockmolecule is the product of the above process. An esterification reactionis then used to attach the rigid biphenyl ester segments to the diblockmolecule containing the random coil and flexible spacer blocks. (Mooreand Stupp). This action involves several deprotection steps as well, toadd additional units of the biphenyl ester segments. To create an objectwith holes, one synthesizes the triblock molecule but with a flexiblespacer that does not have a group that can form crosslinks.

FIG. 4A provides a representation of the mushroom shaped object preparedupon self-assembly of the above described precursor molecules, whileFIG. 4B shows the resultant nanoporous structure produced uponseparation of the non-crosslinked compounds from the structure.

It is evident from the above results and discussion that improvedprocess for fabricating porous nanostructures is provided. The subjectmethods are self-assembly methods and, as such, do not require elaborateor expensive laboratory equipment to perform. The nanostructuresproduced by the subject methods are consistent in terms of size,porosity and pore diameter. In addition, the structures have pores ofsmall diameters, where the methods allow one to tailor the objectsproduced to have particular pore sizes of interest. The structuresproduced by the subject methods find use in a variety of differentapplications, including electronic, analytical and biotechnologyapplications. Accordingly, the subject invention represents asignificant contribution to the art.

All publications and patent applications cited in this specification areherein incorporated by reference as if each individual publication orpatent application were specifically and individually indicated to beincorporated by reference. The citation of any publication is for itsdisclosure prior to the filing date and should not be construed as anadmission that the present invention is not entitled to antedate suchpublication by virtue of prior invention.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it is readily apparent to those of ordinary skill in theart in light of the teachings of this invention that certain changes andmodifications may be made thereto without departing from the spirit orscope of the appended claims.

1. A nanoporous structure produced by a method comprising: (a) combiningfirst and second self-assembling molecules under conditions sufficientfor said first and second molecules to self-assemble into an orderedcomposite structure of said first and second molecules held together bynon-covalent interactions, wherein said first molecules include across-linking functionality that is lacking in said second molecules;(b) covalently bonding said first molecules via said cross-linkingfunctionality to produce a stabilized composite structure; and (c)separating said second molecules from said stabilized compositestructure to produce said nanoporous structure.
 2. The nanoporousstructure according to claim 1, wherein said nanoporous structure hastwo or more nanopores.
 3. The nanoporous structure according to claim 2,wherein said two or more nanopores are uniform and regularly positionedin said structure in a regular pattern.
 4. The nanoporous structureaccording to claim 1, wherein nanopores of said nanoporous structurehave an inner diameter that does not exceed about 5 nm.
 5. Thenanoporous structure according to claim 1, wherein said structure is asheet.
 6. The nanoporous structure according to claim 1, wherein saidstructure is a nano-object.
 7. The nanoporous structure according toclaim 1, wherein said first and second self-assembling molecules arelinear molecules.
 8. The nanoporous structure according to claim 7,wherein said first and second linear self-assembling molecules have alength of from about 4 to about 50 nm.
 9. The nanoporous structureaccording to claim 1, wherein said first molecule comprises a singlecross-linking functionality.
 10. The nanoporous structure according toclaim 1, wherein said first molecule comprises two differentcross-linking functionalities.
 11. The nanoporous structure according toclaim 1, wherein said first and second molecules are organic molecules.12. The nanoporous structure according to claim 1, wherein saidseparating step (c) comprises immersing said stabilized compositestructure in a solvent for said second molecules so said secondmolecules separate from the remainder of said structure. 13-15.(canceled)
 16. An article of manufacture that includes a nanoporousstructure according to claim
 12. 17. A kit for use in a producing ananoporous structure, said kit comprising: (a) first and secondself-assembling molecules that self-assemble upon combination into anordered composite structure of said first and second molecules, whereinsaid first molecules include a cross-linking functionality that islacking in said second molecules.
 18. The kit according to claim 17,wherein said first and second self-assembling molecules are linearmolecules.
 19. The kit according to claim 18, wherein said first andsecond linear self-assembling molecules have a length of from about 4 toabout 50 nm.
 20. The kit according to claim 17, wherein said first andsecond molecules are organic molecules.